Recent posts

Subnetting Made Easy, Part 5

October 04, 2015 | 4 minute read

After publishing my previous post, I received another e-mail from the author of the original e-mail: … So basically, I would like to find out how to find the first usable IP address. As I say, using your process, I can figure out the Network IP address, and the Broadcast IP address, but I don’t know how to figure out the first usable IP. I was...

Subnetting Made Easy, Part 4

October 02, 2015 | 3 minute read

Recently I received the following e-mail from a reader: I have read, and followed your method of finding subnet mask addresses, and calculating the first and last and broadcast addresses, but there is something that I would like to ask. I can follow the “normal” /30 method, using borrowed bits from the fourth octet, but I find it difficult to ...

A Deep Dive in OSPF LSAs, Part 7

April 28, 2015 | 6 minute read

So far in this series I’ve covered Type 1, 2 and 3 LSAs. Next I’m going to cover Type 4 and Type 5 LSAs with the help of this topology. Before we get started though, let’s have a quick refresher on what these LSAs are used for: Type 4 – ASBR-Summary LSA – this is needed because Type 5 External LSAs are flooded to all areas and the detaile...

A Deep Dive in OSPF LSAs, Part 6

April 24, 2015 | 5 minute read

Up until this point I have only covered Type 1 and Type 2 LSAs in this series. I’m guessing by now you must be quite familiar with them and are interested to hear about the other LSAs, so let’s move onto Type 3’s. This is what Wikipeda has to say about Type 3 LSAs: Type 3 – Summary LSA – an Area Border Router (ABR) takes information it has ...

A Deep Dive in OSPF LSAs, Part 5

April 24, 2015 | 5 minute read

In Part 3 I demonstrated how you can use Type 1 and Type 2 LSAs to map the topology an OSPF area. In this post we’ll do the reverse. By looking at a network diagram below, you should be able to determine the following: Who will be sending Type 1 LSAs? How many Type 1 LSA entries will there be? What will the “Link Count” be for each of th...